Traditional internal combustion engines rely on a connecting rod for transmitting combustion power from a piston main body to a crank shaft of the engine. Connecting rods are typically arranged with a first end having an opening or aperture and a second end larger than the first end, which includes a bearing cap that is attached to the second large end and creates an aperture when assembled. Generally, the first small end aperture is connected to the piston, while the second large end is connected to the crank shaft. Typically, a metallic bearing will be positioned either around the crank shaft or within an aperture contact surface of the connecting rod second end and the bearing cap. This provides a rotating surface between the connecting rod and the crank shaft.
The connecting rod second end and bearing cap each include corresponding openings that allow a fastener to secure the bearing cap to the connecting rod second end. When a fastener is a bolt, the opening within the bearing cap may be threaded to receive the bolt. It may also be a stud. Accordingly, the connecting rod may be secured to the crank shaft with the fasteners.
The fasteners are generally mass produced and may include a corrosion resistant coating to minimize material breakdown during shipping and storage. The fasteners may include application of a friction material such as an adhesive coating to the threads in the case of a threaded bolt received in a mating threaded opening to facilitate a more permanent connection of the connecting rod second end and bearing cap.
In theory the adhesive coating increases friction between the threads of the fastener and the corresponding threads in the second end of the connecting rod to keep the fastener in place after assembly. In practice, however, use of an adhesive coating has generally been unreliable. For example, the adhesive may not be uniformly applied such as by way of dipping operations typical of such coating applications. Additionally, fasteners coated with an adhesive coating may be damaged during shipping, e.g., by rubbing against adjacent fasteners within packaging, causing the adhesive coating to wear off. In some situations, moreover, the corrosion coating may interact unfavorably with the adhesive coating, minimizing the effectiveness of the adhesive coating. Flaws within the fastener opening or to the fastener itself may also hinder effectiveness.
Even if the adhesive coating is appropriately applied to a fastener there are other challenges. For example, there is a possibility of shearing the coating off of the fastener during insertion, which may result in an uneven coating layer on the fastener and a build-up of coating under the head of the fastener in the case of a bolt. The build-up of coating at the mating surface between the fastener head and the bearing cap may cause inconsistencies in applying torque to the fastener during assembly, resulting in uneven load distributions and potentially catastrophic failure of the fastened joint.
Any of these foregoing issues may lead to unscheduled maintenance of an engine to re-tighten and/or re-apply the adhesive coating even after assembly is complete. Accordingly, there is a need for a more uniform application of a friction material, e.g., adhesive coating, at the fastened joint between the connecting rod and the bearing cap that is economical for mass manufacturing applications.